Papa Tom

I have a 1996 GT Outpost steel mountain bike that I keep in tip-top shape and still ride everywhere. It has its original rigid fork and its original front cantilever brake assembly.

Lately, I've noticed what I can only describe as "stuttering" when I apply the front brake. I haven't paid much attention because I assumed it was the brake pad catching a rough spot on my rim or something like that, and I planned to get around to looking at it before an overnight ride I took this weekend.

Well, I never got around to it and I took off on this fairly hilly ride that included some good downhills where I was doing maybe 25mph(?) fully loaded with my overnight bags. While coasting downhill, any time I pumped my brakes more than lightly, the stuttering got really bad, and when I took a good long look, I noticed that the front fork was actually flexing while this was happening. Now I'm no longer looking at the brakes and the rim, but at a possible problem with the fork itself.

I just got home and haven't had time to put the bike on my rack yet for a check-up, but I did do some troubleshooting while in my hotel. I checked for cracks in the fork and nothing jumped out at me. The way this thing was jumping forward on those downhills made me suspect a crack was a good possibility, either now or in the future if I don't resolve the issue. I also hand-tested the tightness of the rings that hold my (quill) stem in place and they were tight. Of course, I also checked that the caliper brake assembly was secure.

Before I take the bike apart and check the bearings, etc., does anyone reading this already know exactly what the problem is? It's nothing I've had before. And if you suspect it's the fork, is there a definitive method to check for cracks?

nfmisso

There are many possible causes, with worn headset bearings being the most common/likely.

Other possibilities: brakes loose on the posts, loose posts, loose brake bolts, front rim loose in the fork, front wheel hub bearings, drop out attachment to fork, steerer tube attachment to fork, brake pads are some possibilities, there are likely others.

fietsbob

My AlAn Cyclo cross bike fork did that.. A lot..

try a V brake? * the long cable as a bowstring and flexible fork blades were not a great combo..

*Lennard Zinn, author, VeloNews Tech writer , and Pro Bike custom builder,
did that on his CX race bike.

(post 11 went to find reference)

perhaps add a booster arch? a light fork's posts splay outward
with brake forces applied pushing inward against the rim..




...

Colnago Mixte

Probably not the fork itself, I would bounce the bike around on the front wheel and see if anything sounds loose, buzzes, rattles, or makes an unusual noise. Apply the front brake and rock the bike forward and back to see if brakes or headset have any "slop".

As the poster above sad, it could be any one of a number of things.

Papa Tom

Yeah, I think I'm going to drop the fork and check all of the above. My fear is that, even if a cracked fork wasn't the original problem, all that flexing may have weakened it somewhat. Looking at the welds, I see what appear to be scratches, but not cracks. When I take it all apart, I'll look again, this time with my cheater glasses on!

Papa Tom

Did all these things on the road and in my hotel room. All negative.

Colnago Mixte

I've seen the reinforced forks that 90's steel ATB's have, and they quite are massive. Probably designed to withstand having a 600 lb Sumo wrestler ride off the roof of a house 3 or 4 times. I would love to be wrong, but I doubt the fork is damaged.

zacster

Check for oil on the rim or pads. Also, check the pads for age. Old dry pads may not grip consistently.

Papa Tom

I was going to change the pads before I left, but then I checked them and they still had a lot of meat on them. No oil on the pads or the rim. Good call, though.

Shimagnolo

I'm guessing this has a brake hanger mounted up at the stem?
(Or a stem that has a hole through it so it doubles as a brake hanger.)
If so, replace it with a fork-crown-mounted hanger. Example: https://www.amazon.com/Tektro-Front-.../dp/B006GHDRYC

Full explanation here: https://www.velonews.com/2010/09/new...o-cross_101807
BTW The taller the frame, the worse it makes the problem.

Been there; Done that.
My canti-equipped bike was trying to kill me coming down Flagstaff Mt until I went to a fork-crown hanger.

kaos joe

From Leonard Zinn's column at VeloNews,

"As the brake is applied, the ground applies a force directed backward on the tire, causing the fork to flex backward. Problem is, the brake cable is fixed at one end at the brake caliper and at the other end at the cable stop above the headset (as you can see in my case, at a cable hanger attached to a bolt on the stem face plate).
Think “bow and arrow” and imagine the fork between the cantilever bosses and the top of the headset is like the bow, and the cable is like the string. As the fork flexes back due to braking, the cable tightens like the string in the bow, because its two ends – the cable hanger and the brake calipers, have moved further apart. So even though you may have pulled the brake lever carefully enough to modulate it properly, as soon as the pad slows the wheel down, the fork flexes back and tightens the cable, which in turn pulls the pads harder against the rim. This in turn flexes the fork back further, which tightens the cable more, which pulls the pads harder against the rim, and so on.
Eventually, something has to give: Either the tire must slip on the ground, the rider must go over the handlebars, or the pads must break free from the rim. It is the latter that creates the shudder, the pads bind and release, bind and release, each time allowing the fork to flex back and forth and the tire to roll and stop, roll and stop."



This used to happen on my Atlantis touring bike, but ONLY when the additional weight of a touring load was present. The solution was one of these, which eliminated the issue entirely.

https://www.jensonusa.com/globalassets/product-images---all-assets/tektro/br245k02.jpg


Ahh, I see Shimangnolo beat me to it! All good.

79pmooney

Don't rule out the fork failing. Steel fork blades cracking at the top, just under the fork crown will feel exactly as you describe.

BTDT. I finished a ride with that stutter. Took the wheel off and checked it. It was perfect. Spread the forkblades with my hands. One bent out 8" with about a pound of force. Crack 3/4s of the way around. Similar on the other side but only 1/4. That stutter was the warning.

Ben

Papa Tom

All good info, although it has my head spinning, as I still have a bit of a dehydration headache from the trip home (that's another story). I will take another look at what's been posted here tomorrow and consider everything you guys have suggested. Thank you!

Colnago Mixte

I think if your brake pads are toeed-in wrong (back end of the pad catching first, rather the the front edge of the pad making contact first) that could cause a high speed shudder. I think that's one of the simplest possibilities, so therefore most likely.

It's something that might not become apparent until you attempt a high speed downhill stop. You say your bike was fully-loaded too? Certain things on a bike you can't properly tune up without a hill to test out the part. I live in the flatlands, where it's impossible to check things like how well your FD drops into the granny gear under pressure, and how brakes will react at 40+ mph while flying down a hill.

You're loaded down with bags, so that's gonna stress every part of the bike that much more.

Papa Tom

I'm not in front of the bike right now, but I'm pretty good with bicycle mechanics (at least on MY bike!), so I'm going to go out on a limb and say that the pads are probably toed in correctly, especially since my braking is fine and I'm not getting any squealing. I assume you are saying that the stuttering of the fork might be a symptom, rather than the cause of the problem. Am I correct?

Again, I will look into all these things, but I've observed that the calipers are not jerking back and forth, which leads me to believe it's not a loose brake part or anything to do with brakes, for that matter. Fortunately, though, I am adept enough at this stuff to evaluate all these components and come up with a diagnosis. I just need to find a little free time!

Overall, based on the responses I've gotten, I am satisfied that there isn't one sure cause of the problem. Thanks for settling THAT part for me.

Colnago Mixte

I'm just saying if the brake pad is grabbing and releasing due to bad contact with the rim, that could cause the problem you describe. But you have a huge advantage by having the bike right in front of you, I'm certain you will figure it out before much longer.

70sSanO

cpach

There are a number of causes, but a fork mounted cantilever hanger is relatively inexpensive and will solve a number of them. I'd recommend one.

dsbrantjr

I agree, it is a cheap and easy thing to do and has always worked well for me. I now routinely install crown-mounted hangers on my canti-equipped bikes. Specialized used to make a nice one, but the Tektro and others will do fine.

Papa Tom

OK, I bought and installed the Origin 8 fork-mounted cable hanger. What a pain in the butt trying to find a cable ferrule to fit in to the top of that thing! I ended up winging it and will have to go back to the LBS to get the right one.

I know I should have done one repair at a time to determine what was really wrong, but I wanted to ride the bike to work tomorrow, so while I had the front end apart, I replaced the steerer tube bearings, installed a new front brake cable (the pads are still good), greased and tightened everything up, gave the brakes an adjustment (including toeing), and got on.

So far, it seems better, but I won't really know until I get some speed up on a downhill tomorrow and hit the brakes. I don't really see how the cable hanger could have solved anything, so I'm wondering if all the front end needed was some grease and some additional tightening (when I wasn't exhausted from the overnight ride). We'll see.

Shimagnolo

Then you didn't read post #11 . (Which is an excerpt of the link in post #10 ).

Papa Tom

I did read both of those posts, although I must admit that I'm more of a "visual" person and kind of got lost in the written description. It seemed like it was describing a different issue in which the brake assembly actually moves with the wheel when applied.

Anyway, I'm not gonna argue with you that #11 may have gone over my head because I think you are correct. I can't get my head around how installing the new hanger could have made any difference, but if it works, I don't need to understand it!

Shimagnolo

I'll try another explanation:

Papa Tom

Nope...the pic didn't work. 'Not trying to be a wise guy. It just didn't do it for me.

If it's that the tension on the brakes is suddenly, after 22 years, pulling the canti's so tight that they are, in turn, dragging the fork forward, then I still can't see how mounting the cable on the fork would make any difference. That doesn't mean it's wrong; it just means I can't grasp it. I'm only about half as smart as I was before I retired as an international jewelry crimes investigator and went to work for the local township.

Also, why would this be happening NOW, after all these years?

No need to answer, actually. As I said earlier, if it works, I will be happy with that. I am not looking to write a book about bike repair.

curbtender

Take off your wheel and reverse it.